So, the sd card reader is a known working one with the 3ds?
How do you power the wiiu/emmc? Those devices have several different modes of operation.
1. spi mode
2. 1 bit sd mode
3. 4 bit sd mode
The cardreader expects the device to come up in default mode after reset (spi I think)
When the wiiu is powered, it will likely put the emmc in 4 bit sd mode as it's the fastest, and all 4 data lines are connected.
The 3ds has problems accessing it's emmc when a sd card reader is connected to it.
That's likely why the sd card reader recognises it and is able to access it.
I don't know the wiiu behavour with a cardreader connected. Just summing up possible causes of failure.
How do you power the wiiu/emmc? Those devices have several different modes of operation.
1. spi mode
2. 1 bit sd mode
3. 4 bit sd mode
The cardreader expects the device to come up in default mode after reset (spi I think)
When the wiiu is powered, it will likely put the emmc in 4 bit sd mode as it's the fastest, and all 4 data lines are connected.
The 3ds has problems accessing it's emmc when a sd card reader is connected to it.
That's likely why the sd card reader recognises it and is able to access it.
I don't know the wiiu behavour with a cardreader connected. Just summing up possible causes of failure.